RCS Chats from iPhone (IOS 18) broken

[DrewNumberTwo]

A fun problem got brought up that now that Apple surprisingly supports RCS (Google's SMS replacement) and for some reason it does not function on our networks.

I can see in our internet firewall that there is a TCP 5223 session to us.verizon.rcs.telephony.goog (216.239.36.131) from our test client.  That session is valid, I have a 3way handshake, I can see the Server/Client Hello and it would appear from every piece of info I can see this should be working - yet it seems to not be able to send or receive RCS messages.  There is no SSL decryption at play here.

Anyone seem this or dealt with it previously to have any clues about why this might be failing?

[NeilG]

Yep, i'm seeing this as well. Its being denied ( interzone-default)  The RCS is indeed on TCP  5223 SSL for Iphone but appears only for initial handshake or something. Once rcs communication is successful, it then uses 443 for all communication thereafter.  i'm going to assume you have a basic rule for internet outgoing with "application default"   I believe this will block 5223 on ssl.  Create a new rule allow tcp 5223 / ssl  going to the noted IP.  ((216.239.36.131)  and for the devices required.  I've tested this on my 440 and confirmed working. 

[DrewNumberTwo]

We have a proxy in play which complicates things.  We know there is SSL on 5223 and on 443 but are unsure which happens first.  I theorize that the fact that the two ports would exit our network as two different public NATs may be the root of the issue at present.